Two part question.

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marshall409

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Ok so i have a Laney MXD120 112. 120 watts. it has one unmarked speaker output on the back. the manual specifies it, ohms and what not, but not wattage. i read though that plugging a cab in to this does not disable the internal speaker. the internal speaker is a Celestion 70/80. so...the internal speaker only puts out 65 by itself and the speaker output puts out another 65. thats what i assumed, and ive had trouble finding anything that says otherwise. anyone know if im right, or agree with my guess?

okay second question.

i think im gonna have to pick up one of these epiphone valve juniors.i was thinking i could get the head version, and plug it into the speaker in my laney.(ive heard some reviews saying the head version was better, because of some changes epiphone made after releasing the combo) so thats easy. and i then i got into thinking about being able to switch easily, with an a/b box. so.
laney out>---A/B switcher>Speaker
VJ out>------^

simple enough.(i think)

now, after shopping around online for a/b boxes, ive found that some can turn on both paths at the same time. so what would happen then? the speaker can handle more than the combined wattage of the two amps. but it wouldnt work....would it? plugging two amps into one speaker at the same time?

Adam
 
dont do it

i pluged 2 amps into one speaker once.......... fried both amps...i was young and dumb
 
marshall409 said:
Ok so i have a Laney MXD120 112. 120 watts. it has one unmarked speaker output on the back. the manual specifies it, ohms and what not, but not wattage. i read though that plugging a cab in to this does not disable the internal speaker. the internal speaker is a Celestion 70/80. so...the internal speaker only puts out 65 by itself and the speaker output puts out another 65. thats what i assumed, and ive had trouble finding anything that says otherwise. anyone know if im right, or agree with my guess?

okay second question.

i think im gonna have to pick up one of these epiphone valve juniors.i was thinking i could get the head version, and plug it into the speaker in my laney.(ive heard some reviews saying the head version was better, because of some changes epiphone made after releasing the combo) so thats easy. and i then i got into thinking about being able to switch easily, with an a/b box. so.
laney out>---A/B switcher>Speaker
VJ out>------^

simple enough.(i think)

now, after shopping around online for a/b boxes, ive found that some can turn on both paths at the same time. so what would happen then? the speaker can handle more than the combined wattage of the two amps. but it wouldnt work....would it? plugging two amps into one speaker at the same time?

Adam
Click to expand...

OK, first, the wattage is determined by the amp and the total load, not by which output(s) you use. The two outputs are probably parallel wired and equivalent. If you only use one output, all the power goes there, and if you use both, the power is split between them according to the load plugged into each one. If the load is the same (two 8 ohm spkrs, say), then the power is split evenly and the total load is four ohms.

Second, NEVER connect the outputs of two amplifiers to the same spkr cabinet. Large and expensive damage may ensue. Also, if you do this with an A/B box (I don't know why you would want to with two amps of such disparity in power), make sure that the box is passive, not active. An active A/B box is designed to carry instrument or line level signal and has circuitry which will likely blow up if you run an amplifier speaker output through it. This could short out the amplifier output and again cause large and expensive damage to your amp(s).
 
First question ...... no .... the amp puts out 120 watts ....... so if you only have the internal speaker plugged in .... it puts 120 into that ...... if you add another speaker .... then the 120 is split between the two speakers.
This is simplified because the actual amount of wattage the amp puts out changes with the speaker load (impedance) but for the purposes of what you were asking it'll do.

I think plugging two amps into one speaker is a way bad idea .... the problem is not whether the speaker will handle the combined wattages ..... the Valve Jr is only 5 watts ( I have one BTW .... great little cheap amp), the main problem is will you blow your amplifiers into a flaming pile of debris?
A screw up and you end up with the output of one amp going into the putput of the other amp. Not really the kind of load amp designers have in mind. Now, if your gonna turn the amps off while you switch ..... then it would be ok I suppose ....... and it might be that some amps would be tolerant of this. But the only way to know is to either contact the manufacturers or try it........ have your fire extinguisher handy!
:D
 
ok so if you say if i use one output the whole thing goes there, then that means the 1 12 would be getting 120- watts all the time. its not rated for that. so, theyre wired in series? thats what would make more sense to me. it says "add and extension cabinet for "MORE" power. so that seems to me that it would add an additional 65 watts. right?

ok so two amps into one speaker is a no no. got it. so now i was thinking in a live situation, it would sick to have them both into their own cabs, both mic'ed, and panned left and right. i know its not an original idea by any means. but it sure sounds fun to me. oh my feebly imaginative mind................

Adam
 
well it's more complicated than that.
An amp might be rated 60 watts into 8 ohms and 120 into 4 ohm. So if the speaker in the amp is an 8ohm .... then the amps only putting out 60 watts ...... when you add a second speaker in parrallel .... the load drops to 4 ohms and now the amp is putting out 120 watts.
The jacks in your amp are NOT in series because the amp wouldn't make any sound if you didn't have both speakers plugged in ..... series means it goes thru one and then the other before heading back to the amp. So the second jack is definitely parrallel unless it's a stereo amp which you haven't mentioned.
Also ...... it's not too uncommon for speakers to be rated less than the amp can deliver. There's reasons for this but the biggest would be that it's unlikely you'll ever get that amp up enough that it's actually putting out 120 watts.
 
Do not use a a/b box to route the outputs of a tube amp!!! you will end up with an open circuit and a blown transformer. :eek: Sorry if I jumped the gun by failing to read all posts but am in hurry (boss is pissed today) and did not want you to have to buy a shiny new transformer.
 
can anyone explain the WHY that 2 amps-> one speaker = doom?

jsut curious what electronically is happenig in there.

Thanks,
Daav
 
See above. Boss still pissed (not at me, but in general) otherwise would post more.
 
Thanks alot

Lt. Bob said:
well it's more complicated than that.
An amp might be rated 60 watts into 8 ohms and 120 into 4 ohm. So if the speaker in the amp is an 8ohm .... then the amps only putting out 60 watts ...... when you add a second speaker in parrallel .... the load drops to 4 ohms and now the amp is putting out 120 watts.
The jacks in your amp are NOT in series because the amp wouldn't make any sound if you didn't have both speakers plugged in ..... series means it goes thru one and then the other before heading back to the amp. So the second jack is definitely parrallel unless it's a stereo amp which you haven't mentioned.
Also ...... it's not too uncommon for speakers to be rated less than the amp can deliver. There's reasons for this but the biggest would be that it's unlikely you'll ever get that amp up enough that it's actually putting out 120 watts.
Click to expand...

thanks VERY much bob. that totally cleared it up for me.
i think maybe i will either go with the combo or atleast get the head version and its own cab. thanks everybody.

Adam
 
daav said:
can anyone explain the WHY that 2 amps-> one speaker = doom?

jsut curious what electronically is happenig in there.

Thanks,
Daav
Click to expand...
There's gonna be guys that can explain it in more electronic terms than me but I'll give it a go .....
First off .... some amps (especially tube amps) are very sensitive to the loads you're running them into. You've probably heard of frying amps if you run them into say, 2 ohms when they're not rated for it.
So right off the bat ..... if you're running two amps into one speaker and using an A/B to pick which amp is being heard ..... then the other amp is running into nothing ..... no load at all. That, by itself, is enough to damage some amps. Then, when you're actually switching there's gonna be a momentary thing happening to the load as the switcher makes the change. And if you run two amps into one speaker at the same time ..... well not only do you have a weird load going on (not sure what the output impedence of an amp is but it's certainly not 4-16 ohms) plus you actually have power amp out going into what's supposed to be only a power output of the amp. The output of an amp just isn't designed to have several volts of power going into it. That's gonna be a very unnormal load for the amp to be trying to pump juice into.
It's just like those old talk boxes where you switched between the speakers in your amp and the driver in the talk boxes ..... they've been known to take out amps simply because of that momentary load weirdness when you actually make the switch.

So amps can be super sensitive to loading ....
 
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